In an existing backlight module, a light guide plate is usually used to convert a plurality of point light sources or a linear light source into a surface light source. By providing a plurality of microstructures having different density distributions on a side surface of such light guide plate to reflect and/or refract incident light, output light can be emitted as a surface light source through a light exit surface thereof. However, the angular intensity distribution of any light ray emitted from the light exit surface of such light guide plate may present a normal (Gaussian) distribution. Thus, when such light ray is used as a light point of the surface light source, the angular intensity of each light point in the surface light source provided by the existing backlight module may not be uniform. Therefore, there is still room for improvement of the existing backlight module.